OK, I just bought a used 800XT and took the snorkel kit ( slightly homemade PVC unit) and pulled the HMF Optimizer off it . I did not put the OE muffler on it, runs like shit, it is running lean( hot) , dealer laptoped it and said everything looks ok for settings. Pops out both ends, idles good ,WOT is ok too , just off and mid is where it pops and spits. I’m going to reinstall the HMF this next weekend . I surly thought I could run it without it on there ( and did not take it with me) I have no idea what a/m can is on it. I did replace plugs, and I filled it up with non corn Premium fuel. I would assume that fuel pressure would be ok as the WOT does not appear to be starving. anything else I should check? I do have a ’08 650XT, and ’13 1000XTP so I’m sorta comfortable poking around if need be. I did tear this thing apart to remove the snorkel, ( I added the Xmr belt vent extension that puts that into the Rt side dash area). the air box looked unmolested, the small angled plastic on the transmission vent box was trimmed off , but that should not effect anything. I change out a leaking rear valve cover gasket, and change all the fluids.
any help would be great , I’m only able to get at them on weekends, so I’ll make a list and let you know.